It is the purpose of the proposed work to study the extrageniculate visual mechanism with particular reference to: a) the links between thalamus and cortex and b) the functional organization of the thalamus and the most prominent of the midbrain visual waystations, the superior colliculus. Work on thalamocortical relationships is aimed at understanding the general phenomenon of multiple representation of exteroceptive information within the cerebral cortex. Work on the superior colliculus attacks the problem of multiple sensory representation from the standpoint of the ensorimotor interface. Anterograde autoradiographic and retrograde HRP experiments are planned, some of these in conjunction with electrophysiological recording. Histochemical techniques, notably the acetylcholinesterase method, will also be used extensively since they have been shown to provide valuable guides to the extrageniculate thalamic subdivisions in the cat, and to certain features of compartmentalization of the superior colliculus as well.